Field of the Invention
This application relates to the processing of coal and blended coal depolymerizing medium to depolymerize coal and create heavy products, such as binder pitch and pitch coke, as well as a liquid oil comprised of chemical constituents such as naphthalene having an atmospheric pressure boiling point of 270° C. or lower. Liquefaction occurs substantially by depolymerizing the coal and preventing repolymerization processes.
Description of the Related Art
Naphthalene, a valuable chemical feedstock, is difficult to recover from a coal digest. This is evidenced by the data summarized in FIG. 1, FIG. 2, and Table 1. The data show that the naphthalene does not absorb hydrogen to become tetrahydronaphthalene because there is no discernable tetrahydronaphthalene in the post-reaction assay. Hence most of naphthalene must have decomposed. Hence decomposition is proven to be the favored reaction pathway, not hydrogen absorption, at least in this instance.
This is evident from examining FIG. 1, which is a simulated distillation (SIMDIST) curve from coal tar distillate, showing some 12.26% naphthalene content by mass of solvent with boiling point of 218° C. Yet, after depolymerizing bituminous coal in a ratio of two parts coal tar distillate to one part coal, as shown in FIG. 2, the percentage of naphthalene being distilled at the same temperature of 218° C. decreases to 3.82%. Table 1 memorializes the data illustrated in FIG. 1 and FIG. 2, where the data in the columns indicates the Wt % (content by mass) of each listed item that is simulated or measured at each of their respective boiling points, and the leftmost column is for coal tar distillate without coal and the rightmost column is for post reaction distillate and depolymerized bituminous coal. Evidently, the digestion reaction evaporated or destroyed the naphthalene, probably resulting in generation of low molecular weight methane and possibly carbon dioxide, which are considered to be less valuable than naphthalene. Moreover, the generation of gas creates a pressure rise in the reactor, requiring a higher pressure rating of the reactor. Based on a 2:1 ratio of liquid solvent to coal, the mass of naphthalene in the solvent alone is equal to the mass of about 24% of the amount of coal in the input feed. Additional naphthalene is also present in bituminous coal. This suggests that the total loss of naphthalene from coal and coal tar distillate is substantial and cannot be accounted for via hydrogen absorption reactions.
Naphthalene is a useful feedstock for creating fuels including gasoline, diesel, jet fuel and others. Naphthalene may be reacted to form fuel constituents such as methyl naphthalene, tetralin (tetrahydronaphthalene) or decalin (decahydronaphthalene). Hence, an object of the present disclosure is to avoid decomposition of naphthalene in a depolymerization reaction. This is accomplished in the present disclosure by partially distilling the input feedstock blend (i.e., depolymerization medium and coal). In this case, the cut point, or temperature at which distillation is to be terminated, should be about 220° C. to 260° C. at atmospheric pressure; i.e., higher than the boiling point of naphthalene. Lower temperature distillation is possible at lower pressure. This distillation step results in the recovery of most of the naphthalene in the blend of digestion medium. Given that naphthalene (C10H8) has a hydrogen content of 6.25%, it should be replaced by the addition of additional liquid with equivalent or higher hydrogen content in order to maintain fluidity and depolymerization capability.
TABLE 1Gas Chromatograph, Coal (Lower Kittanning/Kingwood),Soybean Oil and Coal Tar Distillate.Post reactionDistillate andCoal TarDepolymerizedDistillateBituminous CoalOnly(after)Boiling PtWt. %Wt. %Benzene00  110.6toluene0.170.05120unided0.630136ethylbenzene0.270139m + p xylene00145styrene00145o xylene0.650.11613 + 4 ethyl toluene0.501651,3,5 trimethyl benzene00benzonitrile00phenol001681,2,4 trimethyl benzene002,3 benzofuran001,2,3 trimethyl benzene00indan0.390.115177indene0.160.19518000190o cresol0.180201m + p cresol0.470non-id002122,4 dimethyl phenol0.190218Naphthalene12.263.82221benzothiophene0.330quinoline00242isoquinoline00methyl benzothiophene0.3702methyl naphthalene1.620.66methyl benzothiophene0.3701methyl naphthalene0.880.390.460.175256Biphenyl0.460.2551.090.415270Acenaphthylene4.014.24Acenaphthene2.280.5250.360.11287Dibenzofuran2.22.0400.375295Fluorene3.133.351.927.575332dibenzothiophene0.442.445.52.08Phenanthrene17.9523.805340Anthracene1.871.9350.451.42carbazole0.921.1713.5615.04375Fluoranthene9.7813.4950.880.745404Pyrene7.369.86501.735398benzo(a)fluorene1.270.74399benzo(b)fluorene1.150.8952.230.135425Benz(a)anthracene0.240.11431Chrysene1.050triphenylene00480Benzo(b)fluoranthene00Benzo(j)fluoranthene00Benzo(k)fluoranthene00>480° C.00100100
Therefore, a need exists for co-producing net liquid products following distillation of ash-free coal liquids created by depolymerization and extraction, and in particular avoiding loss of valuable naphthalene in the process.